1. Field of the Invention
The present invention relates to the discharge structure of a vane rotary compressor.
2. Description of the Related Art
Recently, the use of refrigerants with low GWPs (Global Warming Potentials) has been studied for a prevention against global warming. However, many of low-GWP refrigerants are lower in operating pressure than conventional refrigerants, and hence require large circulating volumes of refrigerant in refrigeration cycles. A compressor for controlling the circulating volume of a refrigeration cycle requires a large displacement. This inevitably increases the size of a compression element portion of the compressor. In contrast to this, car air-conditioning and the like, which have increasingly used low-GWP refrigerants, use vane rotary compressors which use refrigerants with low operating pressures and can achieve space saving.
A conventional vane rotary compressor is constituted by a cylinder having an internal space, a columnar rotor which makes rotary motion in the internal space of the cylinder, a shaft which is integrated with the rotor and transfers rotational force to the rotor, and vanes which are provided on the rotor and slide inside the cylinder together with the rotation of the rotor while the distal ends of the vanes are in contact with the inner surface of the cylinder. This compressor is configured such that a refrigerant is sucked from a low-pressure space into an operating chamber formed from the cylinder, rotor, and vanes through a suction hole, and the refrigerant is compressed in the operating chamber together with the rotation of the rotor and is discharged from the operating chamber into a high-pressure space through a discharge hole.
A discharge valve formed from a plate-like valve is provided in the opening portion of the discharge hole formed on the high-pressure space side. The discharge valve operates such that when the pressure inside the operating chamber becomes equal to or higher than that in the high-pressure space, the plate-like valve opens the discharge hole due to the differential pressure between the operating chamber and the high-pressure space so as to make the operating chamber communicate with the high-pressure space, thereby discharging the compressed refrigerant into the high-pressure space. The discharge valve also operates such that when the pressure inside the operating chamber becomes equal to or lower than that in the high-pressure space, the plate-like valve closes the discharge hole due to the differential pressure between the operating chamber and the high-pressure space so as to partition the high-pressure space from the operating chamber, thereby preventing the compressed refrigerant from flowing back to the operating chamber (see, for example, patent literatures 1 and 2).
The discharge valve prevents the refrigerant from flowing back from the high-pressure space to the operating chamber. On the other hand, however, since the discharge value closes the discharge hole before all the refrigerant is discharged from the operating chamber through the discharge hole, some high-pressure refrigerant stays in the discharge hole even when the operating chamber becomes empty after the high-pressure refrigerant is discharged. For this reason, some refrigerant may flow back from the inside of the discharge hole into the operating chamber and cause a loss. In order to solve this problem, some compressors include a first discharge valve provided in the opening portion on the high-pressure space side of the discharge hole to open and close the high-pressure space and the discharge hole, and a second discharge valve provided in the discharge hole to open and close the discharge hole and the operating chamber. The first discharge valve is formed from a plate-like valve like the conventional discharge valve. The plate-like valve opens and closes the discharge hole. The second discharge valve is formed from a spherical member. The spherical member is locked to the opening portion of the discharge hole open to the operating chamber side to close the discharge hole. When the spherical member moves away from the opening portion, the discharge hole opens. This structure makes it possible to suppress the backflow of the refrigerant from the inside of the discharge hole to the operating chamber (see, for example, patent literature 3).    Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 11-125190 (page 2, FIG. 7)    Patent Literature 2: Japanese Patent Application Laid-Open (JP-A) No. 2003-120563 (page 2, FIG. 7)    Patent Literature 3: Japanese Patent Application Laid-Open (JP-A) No. 2004-156571 (pages 5 to 8, FIGS. 2 and 3)